Ultrasound is widely used in medicine for diagnostic and therapeutic applications. Therapeutic ultrasound may induce a vast range of biological effects at very different exposure levels. At low levels, beneficial, reversible cellular effects can be produced, whereas at higher intensities, instantaneous cell death can occur. Accordingly, ultrasound therapies can be broadly divided into two groups: “high” power and “low” power therapies. At one end of the spectrum, high power applications include high intensity focused ultrasound (HIFU) and lithotripsy, while at the other end, low power applications comprise sonophoresis, sonoporation, gene therapy, bone healing, and the like.
A popular area in the field of aesthetic medicine is the removal of subcutaneous fat and the reduction of the volume of adipose tissue, resulting in the reshaping of body parts, frequently referred to as “body contouring”. One such technique is a non-invasive ultrasound-based procedure for fat and adipose tissue removal. The treatment is based on the application of focused therapeutic ultrasound that selectively targets and disrupts fat cells without damaging neighboring structures. This may be achieved by, for example, a device, such as a transducer, that delivers focused ultrasound energy to the subcutaneous fat layer. Specific, pre-set ultrasound parameters are used in an attempt to ensure that only the fat cells within the treatment area are targeted and that neighboring structures such as blood vessels, nerves and connective tissue remain intact.
Focused high intensity acoustic energy is also used for therapeutic treatment of various medical conditions, including the non-invasive destruction of tumerous growths by tissue ablation and/or destruction.
For such medical and cosmetic purposes, it is often desirable to be able to focus the ultrasonic output of the transducer. To achieve this, transducers are often comprised of a cup-shaped piezoelectric ceramic shell with conductive layers forming a pair of electrodes covering the convex outside and concave inside of the piezoelectric shell. Typically, the transducers have the shape of a segment of a sphere, with the “open end” positioned toward the subject being treated.
The transducer is excited to vibrate and generate ultrasound by pulsing it, using a high frequency power supply generally operating at a resonant frequency of vibration of the piezoelectric material.
Such a spherical transducer exhibits an “axial focal pattern”. This is an ellipsoidal pattern having a relatively small cross section and a relatively longer axis coincident with a “longitudinal” axis of the transducer, that is, a line through the center of rotation of the transducer perpendicular to the equatorial plane. However, to treat relatively large volumes of tissue, it would be generally advantageous to modify the focal pattern so that it is spread laterally and exhibits decreased intensity along the transducer axis.
Furthermore, since cosmetic treatments in particular, and efficient apparatus utilization in general, are sensitive to the time taken to perform the procedure, methods whereby a singly focused region is moved over the subject's body are unattractive commercially, and better efficacy of such treatments would be desirable.
Other types of transducers are planar in shape, generating a sheet of energy at the target plane, but the focusing power of such transducers is limited. Such planar transducers may also incorporate an acoustic lens to focus energy to a desired location.
Transducers which emit ultrasound in a single focused beam have limitations, such as requiring motion to scan over a treated area larger than their focal region, and such as being generally single-frequencied. This can be overcome by the use of transducer heads comprising several separate emitting sections. Such prior art, multiple segment transducers are generally constructed of a number of separate ceramic piezoelectric elements glued together, or epoxy embedded, in order to produce a single integrated head. However, transducers produced by such methods are generally costly to manufacture because of the labor intensive process of manufacture, and are often unreliable because of the susceptibility of the adhesive or epoxy matrix to loosen, degrade, or otherwise interfere with the transducers under the effects of high intensity ultrasound.
There therefore exists a need for a new transducer and method of manufacturing multi-segmented transducers, and methods of operating such transducers and transducer arrays and system, which will enable novel treatments to be achieved without the potential disadvantages of prior art adhesive-assembled transducers.